On July 31, 1907, 100,000 people lined the Charles River to mark the opening of a new bridge—a rare day of joint celebration between the competitive city governments of Boston and Cambridge. There was a luncheon, a parade, speeches. The fireworks launched from the river at dusk were later described by the Cambridge Chronicle as “unquestionably the finest display ever seen in these parts.”

More than a century later, the bridge they celebrated—known as the Cambridge Bridge at the time, renamed the Longfellow in 1927—is being disassembled, the more than 2,000 granite blocks that form its central towers carried off for cleaning and repair. The $255 million project, and three-year traffic snarl it causes, is intended to finally fix the decaying steel understructure and bring the bridge up to modern code.

To historians and architects, the renovation presents something else: an opportunity to rediscover an underappreciated landmark, a feat of design and engineering that offers a window onto the aspirations of a growing metropolis at the turn of the 19th century.

“[The Longfellow] has a kind of heroism that defines public bridge art,” says Charles Redmon, a Cambridge architect who was a member of the design review commission that oversaw plans for the Zakim Bridge. “It still has a very strong civic stature compared to bridges built today.”

When planning for the Longfellow Bridge began in 1898, there were already eight bridges spanning the Charles River—functional structures designed to carry pedestrians and horse-drawn vehicles across the river, and not much more.

The new span would replace the West Boston Bridge, which had been built in 1793, a time when there were only three farms east of the village at Harvard Square. Over the intervening century, the populations of Boston and Cambridge had exploded, more than doubling between 1860 and 1880. The growth put a strain on the West Boston Bridge, and it also brought a new set of aspirations to Boston—a desire to be a beautiful city as well as a prosperous one. The Charles River Basin was being transformed from a tidal mud flat into the center of a park system, and the new bridge was intended as “an adornment,” wrote Charles Sullivan, executive director of the Cambridge Historical Commission, in an e-mail.

In the fall of 1898, William Jackson, the chief engineer of the city of Boston, and noted architect Edmund Wheelwright traveled to Europe on a research mission. They looked at bridges in Germany, Austria, France, and England, and came back with a simple, classical design.

Franz-Josef Ulm, a professor of engineering at MIT and Longfellow Bridge enthusiast, sees it as a subtle inversion of the towering Brooklyn Bridge, which had been built 15 years earlier. “The Longfellow is a suspended bridge turned upside-down—the load from the deck is carried by beams onto an arch,” says Ulm. “That plays much the same role, just upside-down, as cables that span from pier to pier.”

The result suited Boston perfectly, fusing the ambition of European aesthetics with a practicality that fit its location. “If it were much taller, it would tend to interrupt the flow of civic space around both edges of the river,” says Redmon.

The Longfellow did interrupt one important thing, says Nancy Seasholes, an independent historian who teaches at Boston University. The US government required any bridge over a navigable waterway to allow commercial boats to pass through. The Cambridge Bridge Commission—not wanting to mar the aesthetics of the new bridge by adding a draw—successfully petitioned Congress for a waiver. That, along with the Charles River dam completed a few years later, “closed the Charles River to navigation,” says Seasholes, and turned it into the recreational lake it is today.

It also knitted Boston and Cambridge closer together, carrying the first subway line to connect Boston and Cambridge. Workers from Boston could now take a train to the new “clean” industries sprouting around Kendall Square: printing, publishing, binding, photoengraving.

The Longfellow’s real importance, however, was more symbolic: It was a landmark for a city successful enough to invest in public works with more than just practical value. “It was designed and built in an era of growing national confidence,” Sullivan wrote in an e-mail, “when America was discovering that it could match or exceed European precedents in architecture and urban design.”

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